Analysis of health-related, skill-related physical strength, and physique by blood pressure levels of Korean seniors

In Korea, the prevalence rate of hypertension among people aged over 30 is on an upward trend, which increased from 26.2% in 2008 to 28.3% in 2018. This hovers above the global morbidity rate of hypertension. As hypertension is the cause of cerebrovascular or cardiovascular diseases, early treatment and management are critical. Also, while there has been numerous research conducted on exercise intervention, the number of studies done on hypertension and physical fitness falls far below. To identify the relationship between health and physical fitness depending on the blood pressure levels of Korean seniors, the physical fitness test results of the National Fitness Award 100 conducted in 2017 were used, and blood pressure level, physique, and physical fitness data of 17,110 elderly population aged above 65 were analyzed. IBM Statistics SPSS 25.0 was used to process the collected data. Due to the gender difference in blood pressure levels, physique, and physical strength, the analysis was conducted by each gender, and the analysis of variance (ANOVA) was performed to identify the differences in physique and physical strength depending on the blood pressure level. Also, Tukey’s HDS test was conducted if such differences were found. All analyzes were tested at the significance level (α) of 0.05. As a result of comparing the physique factors by blood pressure level, only males showed a significant difference between groups in terms of height(p = .019), and higher blood pressure implied greater height. Also, for both genders, those with high blood pressure appeared to have greater body weight(p < .001), body fat percentage(p < .001), BMI(p < .001), waist circumference(p < .001), and waist-to-height ratio(p < .001),. In addition, as the result of comparing health-related physical strength and skill-related physical strength by blood pressure level, males showed a significant difference only in muscular strength(p = .026) and flexibility(p < .001), while females showed a significant difference between groups in terms of cardiovascular endurance(p < .001), muscular strength(p = .025), muscular endurance(p < .001), balance, and motor coordination except for flexibility. Holistically, males only showed a significant difference in muscular strength and flexibility while females appeared to have a significant difference between groups in all categories except flexibility, which can be considered that physical fitness factors influence the blood pressure of females more than males.


Introduction
While many international and national organizations have been recommending seniors to carry out the physical activity at least for a minimal amount to maintain health, let alone numerous studies about exercise intervention conducted to identify the importance of physical activity and preventing hypertension, there have not been enough in-depth studies on blood pressure and physical strength.
Therefore, based on the data from the "National Fitness Award 100" of the Korea Sports Promotion Foundation (KSPO), which has been leading the measurement of physical strength by life cycle, this study aimed to identify physical strength factors that can be helpful for the improvement of senior blood pressure and look at the relationship between Korean seniors' blood pressure level and physical strength. It also aimed to provide primary data for the establishment of exercise programs for seniors by blood pressure, accustomed to different situations depending on necessary physical strength factors.

Data and subjects
The study utilized the physical fitness test results of the "2017 National Fitness Award 100" provided by the Korea Sports Promotion Foundation (KSPO). The National Fitness Award of KSPO is an official certification authority designated by the government, which officially performs physical fitness measurement, physical fitness evaluation, exercise prescription, and physical fitness certification. The subjects were seniors aged 65 or above. The total number of subjects was 17,110 (11,855 females, 5,255 males), and the average age was 71.8 for females and 72.7 for males. This experimental protocol was approved by the Institutional Review Committee of Sungshin Women's University (SSWUIRB-2021-036) and informed to and received the consent of all participants. The characteristics of the subjects are as follows.

Blood pressure standard
The blood pressure levels were divided into four groups based on the standards of the Korean Society of Hypertension: below 120/88mmHg as Normal, 120-129/80mmHg as Elevated, 130-139mmHg systolic pressure or 80-89mmHg diastolic pressure as Prehypertension, and 140mmHg or above systolic pressure or 90mmHg or above diastolic pressure as Hypertension [45].

Physique and obesity index
For physique, an automatic weight/height scale (BSM370, In-Body, Korea) was used to measure the height (cm), body weight (kg), and body mass index (kg/m 2 ). Waist circumference (cm) was measured with a tape measure, and body fat percentage was measured with a body composition analyzer (InBody 620, In-Body, Korea) [46].

Physical fitness
Health-related physical strength (cardiorespiratory endurance, muscular strength, muscular endurance, flexibility) and skill-related physical strength (balance, motor coordination) were measured for physical fitness [46].

Cardiorespiratory endurance (two-minute walk-in-place).
The minimum height to which the subject has to raise their knees was set for each subject. Then, the distance between the middle of the knee to the ilium (iliac crest) was measured with a tape measure, after which a tape was used to mark the middle of the femur. With the starting signal, the subject began with their right leg, tagging one knee after another to the rubber string. It was measured as "one time" when both of the legs fully walked for two minutes starting with their right foot. A chance was given for the subject to practice before the measurement, and there were no second measures.

Muscular strength (grip strength).
The subject was ordered to hold a hand gripper with second knuckles of their hand, stretch out their arm forward keeping their body and arm distanced by 15 degrees and grip it as hardest as they could for five seconds with the posture unchanged. The left and right arms were measured twice one after another, and the best score of each was recorded by 0.1kg unit. Then, relative handgrip strength (handgrip strength � body weight ×100) was calculated.
2.4.3 Muscular endurance (sit-to-stand). The subject was instructed to sit in the center of the chair with their back straight and both arms crossed at the wrists and gathered in front of the chest. Then on the mark, the subject was told to fully stand up, and return to a fully seated position. They were encouraged to repeat it as many as they could in 30 seconds, and the total count of full sit-and-stands performed for 30 seconds was recorded. If the subject was in a half-stood position when 30 seconds were over, it was counted as a full stand-up. The measurement was only allowed once.

Flexibility (sit-and-reach).
The subject was instructed to take off their shoes and sit with knees stretched forward until the soles were placed flat against the measurement device. Then, the subject was told to keep their knees pressed flat to the floor with palms touching the box facing downwards, and bend the upper body and extend it as far forward as possible. Measurement was performed twice, and the better record was selected and recorded in units of 0.1cm.

Balance (timed up and go).
A cone was installed at exactly 3m-point from the back of the cone to the frontal edge of the chair (one spot on the floor). The chair was placed against the wall so that it faces the cone, and the subject was instructed to stand up, walk around the cone, then return to the chair to the seated position as fast as they could with the starting signal. The subject was ordered to repeat it twice and was given only one chance for the measurement. The fastest time was recorded in units of 0.1 seconds.
2.4.6 Motor coordination (figure-of-8 walk). A 3.9m (width) × 1.6m (length) rectangle was drawn, and cones were fixed within the side edges, where a chair was placed at the 2.4mpoint from them. The subject was told to stand by, sitting on the chair at the center of the frontal edge of the rectangle, after which was instructed to stand, go around the cone on the right, return to the seated position, stand up right after again, go around the cone of the left, and return to the seated position, with the "start" signal. This course was repeated twice, and the record was measured in units of 0.1 seconds.

Statistical analysis
IBM Statistics SPSS 25.0 was used to process the collected data. Due to the gender difference in blood pressure levels, physique, and physical strength, the analysis was conducted by each gender, and the analysis of variance (ANOVA) was performed to identify the differences in physique and physical strength depending on the blood pressure level. Also, Tukey's HDS test was conducted if such differences were found. All analyzes were tested at the significance level (α) of 0.05.

Analysis of blood pressure by gender
In terms of blood pressure, 41.6% of female subjects were classified into the Normal group, 37.2% in the Elevated group, 16.9% in the Prehypertension group, and 4.4% in the Hypertension group.
For males, 38.5% were classified into the Normal group, 36.4% in the Elevated group, 19.4% in the Prehypertension group, and 5.7% in the Hypertension group. Males showed slightly higher figures in the Prehypertension and Hypertension groups compared to their female counterparts ( Table 1).

Analysis of differences in physique and body fat percentage
The study looked at the differences in height, body weight, BMI, waist circumference, waistto-height ratio, and body fat percentage by blood pressure level. It was found that male seniors showed a statistically significant difference in all physique factors, while female seniors also showed a statistically significant difference in all factors except height.
In terms of males, for body height, the Hypertension group (165.95±6.00) was the tallest, while the Normal group (164.97±5.77) was the shortest(p = .019). Meanwhile, body weight increased with higher blood pressure(p < .001). In short, males with higher blood pressure had higher height with greater body weight. For obesity rate measured with waist circumference and waist-to-height ratio, the Elevated group, Prehypertension group, and Hypertension group showed a high figure. For waist circumference, it was 85.35±7.84 for the Elevated group, 86.34±7.59 for the Prehypertension group, and 86.77±9.76 for the Hypertension group. Meanwhile, for the waist-to-height ratio, the Elevated group recorded 0.54±0.05, the Prehypertension group 0.55±0.05, and the Hypertension group 0.55±0.06 (Table 2). For body fat percentage, the Prehypertension group and Hypertension group recorded 26.46±6.06 and 26.94±6.11, respectively. For BMI, it was 24.61±2.7 for the Prehypertension group and 24.95 ±2.63 for the Hypertension group. In short, the two groups, Prehypertension and Hypertension, showed high figures in body fat percentage(p < .001) and BMI(p < .001), measures of obesity.
For females, the Prehypertension group (58.59±7.73) and Hypertension group (58.59±8.88) appeared to have greater body weight(p < .001). For body fat percentage, the Hypertension group recorded (36.11±6.68), and for BMI, the Prehypertension group recorded (25.10±3.06) while the Hypertension group recorded (25.25±3.63). In short, the Hypertension group was found out to have high figures in terms of body fat percentage(p < .001) and BMI(p < .001). In regards to obesity rate measured with waist circumference and waist-to-height ratio, the Prehypertension group and Hypertension group showed a high figure(p < .001). For waist circumference, the Prehypertension group recorded 83.82±7.76, while the Hypertension group recorded 83.60±9.52. For waist-to-height circumference, the two groups recorded 0.55±0.05 and 0.55±0.06, respectively (p < .001) ( Table 3).

Skill-related physical strength
Male seniors did not show a statistically significant difference in skill-related physical strength by blood pressure levels (Table 6), but female seniors showed a statistically significant difference in motor coordination and balance. A high record of motor coordination was shown in the Hypertension group (26.88±6.53) and Elevated group (26.67±6.40), Prehypertension

Discussion
With With an aim to identify the relationship between physique and physical fitness by blood pressure levels of Korean seniors, this study utilized the physical fitness test results of the National Fitness Award 100 conducted in 2017, analyzing the data of 17,110 subjects aged 65 or above (11,855 females, 5,255 males). Essential (primary) hypertension is mainly caused by living a problematic lifestyle, including lack of physical activity and a wrong diet [47,48], which can accompany diseases such as obesity. Not all hypertensive patients are obese indeed, however, as there is a positive correlation between hypertension and obesity index [49], this study analyzed the relationship between physique and blood pressure. As a result, both males and females showed a significant difference in body weight, body fat percentage, BMI, waist circumference, and waist-to-height ratio, while only males showed a significant difference in height. Such results are in line with the research that taller height leads to increased blood pressure for males more than females [50,51]. Also, the obesity index (BMI, waist circumference, and waist-to-height ratio) increased as the groups of both gender had higher blood pressure, which is in line with the research result which reported that body mass index, waist-to-hip ratio, and waist circumference are higher in the prehypertension group than the normal group [52]. The findings of this study also suggest that obesity is a key predictor of hypertension.
Among the factors for improving life habits, the relationship with health conditions such as physical activity and physical strength, and blood pressure and diabetes have been proven to be highly correlated [53,54]. As explained, since physical activity not only improves diseases but also improves physical strength, this study investigated various health-related physical strength factors according to blood pressure level. As a result, females showed a significant difference in cardiorespiratory endurance, muscular strength, and muscular endurance, while males appeared to have a significant difference in muscular strength and flexibility. Such results were in line with the research that found out systolic pressure, diastolic pressure, average arterial pressure, and cardiorespiratory endurance are in a significant negative correlation [55], and the study that the systolic pressure of aged females between 65-74 is in a negative correlation with cardiorespiratory endurance [56]. This implies that even though high cardiorespiratory endurance cannot entirely prevent the development of hypertension, higher cardiorespiratory endurance can lower the risk of hypertension [57].

PLOS ONE
Analysis of Korean seniors physique and physical strength based on blood pressure A decrease in mean arterial blood pressure during the recovery period after maximum intensity exercise is greater in women, and it was suggested that the decrease in arterial blood pressure of women was due to a greater vasoconstrictor response [58]. Therefore, it was reported that in women, total peripheral resistance is increased by compensatory vasoconstrictor action for a decrease in cardiac output and mean arterial blood pressure [59], and it was identified that strategies for controlling blood pressure of women through exercise are considered to be different from men because the difference in cardiovascular responses to control blood pressure during incremental intensity exercise differ according to gender [60]. Preceding studies have highlighted muscular strength as a physical strength factor to reduce blood pressure as the weakened grip strength among the oldest old leads to increased blood pressure [56]. Also, other preceding research results on the correlation of muscular strength and blood pressure stated that muscular strength was shown to be significantly low in the Prehypertension and Hypertension groups when compared with the Normal group in all age groups [61], and one study on people aged 50-75 reported that systolic pressure has a negative correlation with muscular strength [62]. The findings of this study found out that both male and female subjects showed a significant difference in muscular strength by blood pressure levels, but it was just that the Normal group showed a high level of muscular strength, and no clear pattern based on blood pressure levels was shown. Also, for muscular endurance, females in the Normal group appeared to have the best muscular endurance, showing a trend where the higher blood pressure level led to a significant drop in muscular endurance. Such observations are in line with the study that reported muscular endurance decreases with higher blood pressure [49], but as males did not show a significant difference, it is considered that there needs to be further studies conducted on muscular strength.
The ACSM recommends hypertensive patients to carry out flexibility exercises 2 to 3 times a week along with aerobic and resistance exercises in its guidelines [63]. Also, it is reported that high flexibility can lower the prevalence of hypertension [64]. In regards to flexibility, only males showed a significant difference by blood pressure, where the Prehypertension group appeared to have the greatest flexibility and the Normal group had the lowest. Such results were identical to the research that flexibility increased significantly in the order of Prehypertension group, Elevated group, and Normal group for males aged 60 or older [61]. Flexibility is an important physical fitness factor for muscle stretch and joint mobilization [65], but for aged males, blood pressure and flexibility were in a negative relationship.
Age-related increase in systolic blood pressure and pulse pressure accelerates after middle age [66]. Similarly, trunk flexibility has been reported to deteriorate faster after middle age, based on 6000 flexibility results [67]. Blood pressure is dependent on arterial wall stiffness, and collagen fibers in the arterial walls are involved in the stiffness [68]. In addition, when comparing the physical fitness of men and women of the same age, flexibility is the only measure of physical fitness where women score higher than men [69]. Women also generally have lower blood pressure than men of the same age [66]. These factors may be related to the fact that women have less connective tissue collagen [70] and a much less age-related effect on the stiffness of collagen material parameters in women [71]. Clarifying these mechanisms requires further research. As in this study, it is not easy to compare preliminary studies with this study because the research on various physical factors according to blood pressure level is very insufficient. However, in a similar preliminary study [49], muscular strength, muscular endurance, balance, flexibility, and cardiovascular endurance of normal blood pressure group, early high blood pressure group, and stage 1 high blood pressure group were compared, and the results of the study identified that early high blood pressure group has the best muscular strength and flexibility. Also, in the study by So & Choi [43], the difference in physical strength level according to high blood pressure standards was investigated, and as a result, men in their 60s, early high blood pressure group showed the best results in muscular endurance, speed, agility, and balance. In a study by Kim et al. [72] conducted in 2022 on men and women over 65 years of age (218,848 people) that measured muscular strength, muscular endurance, cardiovascular endurance, balance, coordination, and flexibility and gave Level 1.
In a study conducted by Kim, Bong Ju et al in 2022 on men and women over 65 years of age (218,848 people) that measured muscular strength, muscular endurance, cardiovascular endurance, balance, coordination, and flexibility and gave level 1 if above 70th quintile, level 2 for above 50th quintile, level 3 for above 30th quintile, and the rest level 4, the result turned out to be the opposite of what is generally expected that the blood pressure would be lower when fitness level is hgher. It is believed that follow-up studies are needed for clearer identification because there are still various opinions in the studies on flexibility.
According to the results of analyzing skill-related physical fitness by blood pressure, males did not show differences between groups, while females showed differences in motor coordination and balance. Females' motor coordination and balance were all higher in the Elevated, Prehypertension, and Hypertension groups than the Normal group. In other words, females with higher blood pressure can be regarded to have poor motor coordination and balance. For balance, those aged between 65-75 showed a significant positive correlation between systolic pressure and balance [56], which was in line with the research which reported that balance (p = 0.006) increased with higher blood pressure [49]. Furthermore, among the preceding research on motor coordination and balance after exercise intervention conducted on hypertensive patients, studies that showed that the systolic pressure of the Hypertension group significantly dropped after participating in an exercise program and that motor coordination and balance significantly increased making improvements [73] support the findings of this study.
In sum, males only showed a significant difference in muscular strength and flexibility, while aged females showed a significant difference between groups in all categories except flexibility. It is necessary to develop various gender-based exercise programs that take other physical factors of women and men into account because women have multiple body functions that decrease faster than men [49,[62][63][64] and have a higher rate of dysfunction than men [74]. In particular, it is believed that exercise prescription for controlling blood pressure of women should be made differently from men because women show a higher heart rate change than men to maintain cardiac output that serves to supply oxygen and nutrients to the muscles that are active during exercise.
Lastly, the 8th report of the Joint National Committee, which suggests guidelines for the treatment and management of hypertension, recommends patients to consistently carry out lifestyle interventions across their overall efforts for managing health. It is important to create a healthy lifestyle for the management of hypertension [5]. In particular, as regular exercise is told to be a safer way of lowering blood pressure compared to drug treatment [75], it is considered that various exercise programs need to be developed and suggested to hypertensive patients, on top of aerobic exercise, reflecting physical strength factors and individual preferences as proved in this study to more effectively prevent and improve hypertension.

Conclusion
This study intended to investigate the association with various physical strength factors that can help to improve blood pressure of the elderly by analyzing health, technology-related physical strength, and physique by blood pressure level of the elderly in Korea, As a result of the study, it was identified that the blood pressure level of the elderly differed in physical strength factors according to gender.
As the results of the study, the blood pressure levels of seniors differed greatly by physical strength factors by gender. While males showed a significant difference in only muscular strength and flexibility, females showed a significant difference between groups in health and skill-related and physical fitness (cardiorespiratory endurance, muscular strength, balance, motor coordination) except flexibility, which implied that they are valid indicators for the management of blood pressure. Hence, the results of the study are expected to be used as primary data for the development of exercise programs for the prevention and improvement of hypertension considering the gender difference and various physical strength factors. However, there were limitations as the study was cross-sectional research, and comorbidities and treatment history could not be identified. There is a need for an epidemiological study to examine the association.